Medication dispensing apparatus configured for rotate to prime and pull/push to inject functionality

ABSTRACT

A medication dispensing apparatus having a manually operable plunger axially shiftable relative to the apparatus housing. The plunger is pullable relative to the housing in a proximal direction to cock the apparatus, and when the plunger is then manually pushed back toward the housing, a piston within a medicine container of the apparatus is shifted to force medication from a needle assembly at the distal end of the apparatus. The medication dispensing apparatus also includes a priming mechanism which is operated by rotating an externally accessible driver portion to prime the apparatus for use, which priming can be performed whether or not the apparatus is in a cocked state.

BACKGROUND OF THE INVENTION

[0001] The present invention pertains to medication dispensing devices,and, in particular, to a portable medication dispensing device such asan injector pen.

[0002] Patients suffering from a number of different diseases frequentlymust inject themselves with medication. To allow a person toconveniently and accurately self-administer medicine, a variety ofdevices broadly known as injector pens or injection pens have beendeveloped. Generally, these pens are equipped with a cartridge includinga piston and containing a multi-dose quantity of liquid medication. Adrive member, extending from within a base of the injector pen andoperably connected with typically more rearward mechanisms of the penthat control drive member motion, is movable forward to advance thepiston in the cartridge in such a manner to dispense the containedmedication from an outlet at the opposite cartridge end, typicallythrough a needle that penetrates a stopper at that opposite end. Indisposable pens, after a pen has been utilized to exhaust the supply ofmedication within the cartridge, the entire pen is discarded by a user,who then begins using a new replacement pen. In reusable pens, after apen has been utilized to exhaust the supply of medication within thecartridge, the pen is disassembled to allow replacement of the spentcartridge with a fresh cartridge, and then the pen is reassembled for itsubsequent use.

[0003] For an injector pen to be used optimally, just prior to using thepen to inject oneself with medicine, a user should prime that pen.During priming, the pen is operated to shift the cartridge piston asufficient distance to force any air from the cartridge and needle andcause medicine to reach the exposed distal or forward tip of the needle,such that the subsequent injecting use of the pen in fact delivers thevolume of medicine the pen is arranged to deliver. Some users, however,fail to so prime the pen, resulting in an injecting of less medicinethan presumably intended by the user.

[0004] One possible explanation for the failure to prime is that thedesign of most injector pens does not assist the user in conceptuallydistinguishing a priming step from a dose injecting step. In particular,the priming step typically involves setting the pen to deliver a smalldose, operating the pen without injecting the user but otherwise in thesame manner as would be performed during user injection, and thenrepeating these steps if necessary, until priming has been accomplished.Then, during the dose injecting step, the dose is actually set inexactly the same way as in the priming step but typically in a largerquantity, and then the pen is used to inject the medicine into the user.

[0005] U.S. Pat. No. 5,961,495 discloses an injection pen in which thepriming control mechanism is by outward appearances distinct from themechanism used to actually set and then inject the selected dose into auser. Dose setting and injection is accomplished with a dose knob at theproximal end of the pen housing. The dose knob is rotatable to set oneof a number of dose quantities which are possible to select. Injectionof the set dose is accomplished by pulling out the dose knob, and thenpushing the knob in after the pen has been manipulated such that itsinjection needle has penetrated the user's skin. The priming mechanismutilizes a manually operable priming control sleeve that is spaced fromthe dose knob. The priming control sleeve is connected to the internaldrive mechanism of the pen such that the sleeve can be manuallyrotationally pivoted back and forth as necessary to prime the pen inanticipation of the injecting operation. While perhaps functional, thisdesign is not without its shortcomings. For one thing, the adjustabilityin the setting of the dose to be injected results in a relativelycomplicated pen design, which may undesirably increase the cost ofmanufacture and assembly of the pen. The back and forth ratchetingaction of the priming control sleeve possibly required to achieve penpriming also may be confusing or not intuitive to some users, who mighttherefore fail to prime the pen completely. In addition, the dosesetting capacity of the pen is a potential source of dosing errors asthe user who intends to inject the same quantity of medicine as injectedthe last time the pen was used may fail to pay proper attention to thedose actually set, which set dose may be different than what was setpreviously as a result of an inadvertent switching since the prior use.

[0006] Thus, it would be desirable to provide an apparatus thatovercomes these and other shortcomings of the prior art.

BRIEF SUMMARY OF THE INVENTION

[0007] In one form thereof, the present invention provides a medicationdispensing apparatus including a housing, a fluid container mounted tothe housing and defining a medicine-filled reservoir, a needle assemblyremovably attached to a distal end of the fluid container to have aninjection needle of the needle assembly in flow communication with thereservoir, and a drive mechanism for dispensing a dose of medicine fromthe reservoir through the injection needle, which drive mechanismincludes a plunger that is manually pullable relative to the housing ina proximal direction to shift the apparatus from a ready state to acocked state, and which is manually pushable relative to the housing ina distal direction to force medicine out the injection needle whilereturning the apparatus from the cocked state to the ready state. Theapparatus includes a priming mechanism for priming the injection needlewith medicine from the reservoir, which priming mechanism includes adrive portion external to the housing to be manually rotatable relativeto the housing. The apparatus further includes a rotation controllingmechanism that permits manual rotation of the priming mechanism driveportion in a first direction and as far as necessary to achieve priming,and that prevents manual rotation of the priming mechanism drive portionin a direction opposite to the first direction.

[0008] In another form thereof, the present invention provides amedication dispensing apparatus including a housing, a fluid containermounted to the housing and defining a medicine-filled reservoir, aneedle assembly removably attached to a distal end of the fluidcontainer to have an injection needle of the needle assembly in flowcommunication with the reservoir, a drive mechanism for dispensing adose of medicine from the reservoir through the injection needle, whichdrive mechanism includes a plunger that is manually pullable relative tothe housing in a proximal direction to shift the apparatus from a readystate to a cocked state, and which is manually pushable relative to thehousing in a distal direction to force medicine out the injection needlewhile returning the apparatus from the cocked state to the ready state.The apparatus includes a priming mechanism for priming the injectionneedle with medicine from the reservoir by manually rotating an elementother than the plunger, and the priming mechanism is operable to effectpriming whether the apparatus is in the cocked state or the ready state,and without altering the dose to be dispensed by the drive mechanism ifthe apparatus is in the cocked state.

[0009] In another form thereof, the present invention provides amedication dispensing apparatus including a housing, a fluid containermounted to the housing and defining a medicine-filled reservoir with amovable piston at a proximal end, a needle assembly removably attachedto a distal end of the fluid container to have an injection needle ofthe needle assembly in flow communication with the reservoir, a drivemember axially extending within the housing and movable distally toadvance the movable piston toward the injection needle, which drivemember, along an axial cross-section, has a series of axially spacedprojections, a follower portion engagable with the projections andhaving a resilient construction, and a plunger operably connected to thefollower portion and manually pullable in a proximal direction to shiftthe plunger from a first position to a second position, and manuallypushable in a distal direction to shift the plunger from the secondposition to the first position. The follower portion is axiallyshiftable by movement of the plunger in the proximal and distaldirections. The follower portion bends radially outward and axiallyslides over at least one projection of the drive member when the plungeris pulled proximally to shift from the first position to the secondposition, and the follower portion, by abutment with a projection of thedrive member over which the follower portion previously slid, advancesthe drive member distally when the plunger is pushed distally from thesecond position to the first position. The apparatus further includes apriming driver operably connected to the drive member and including adrive portion external to the housing which is manually rotatableindependently of the plunger to axially advance the drive member toprime the injection needle with medicine from the reservoir.

[0010] In still another form thereof, the present invention provides amedication dispensing apparatus including a housing, a fluid containermounted to the housing and defining a medicine-filled reservoir with amovable piston at one end and an outlet at the other end, a drive screwwith external threading and axially extending within the housing andmovable distally to advance the movable piston toward the outlet, atleast one anti-rotation member operably engaging the drive screw toprevent rotation of the drive screw within the housing, and a primingdriver axially retained relative to the housing and having a firstportion and a second portion, the first portion internal to the housingand in threaded engagement with the drive screw, the second portionexternal to the housing to be manually rotatable, whereby rotation ofthe second portion rotates the first portion to force the drive screw totranslate distally. The apparatus further includes a follower and aplunger. The follower is axially movable relative to the priming driverand rotatably fixed thereto, and includes a portion internal to thehousing and in threaded engagement with the drive screw. The plunger isaxially movable relative to the housing between a distal position and aproximal position. The plunger includes a manually graspable gripportion which is pullable proximally to move the plunger from the distalposition to the proximal position, and the plunger is connected to thefollower to allow relative rotation therebetween and to shift thefollower axially when the plunger moves back and forth between thedistal and proximal positions. Each of the follower portion and thepriming driver first portion has a resilient construction, whereby whenthe plunger is pulled from the distal position to the proximal positionto shift the follower proximally, the follower portion slides over thethreading of the drive screw that is being axially retained byengagement with the priming driver first portion, and whereby when theplunger is pushed from the proximal position to the distal position toshift the follower distally, the priming driver first portion slidesover the threading of the drive screw that is being axially advanced byengagement with the follower portion.

[0011] One advantage of the present invention is that a medicationdispensing apparatus can be provided which is to be primed in afundamentally different manner than the manner by which it is to be usedto inject a dose of medicine, thereby providing a user with an aid toremembering to prime the apparatus prior to injection.

[0012] Another advantage of the present invention is that a medicationdispensing apparatus can be provided which can be easily primed using amanually rotatable element, and easily used to inject a dose by manuallypulling out and then pushing in a plunger.

[0013] Another advantage of the present invention is that a medicationdispensing apparatus can be provided which delivers a fixed dose, andtherefore does not require any dose setting feature which could beaccidentally altered prior to use to cause an incorrect dose to bedelivered.

[0014] Another advantage of the present invention is that a medicationdispensing apparatus can be provided which can be made from a smallnumber of parts so as to be relatively inexpensive to produce, andthereby more justifiably disposable after its medication contents areexhausted.

[0015] Still another advantage of the present invention is that amedication dispensing apparatus can be provided which due to it beingmade from a limited number of parts, lacks any large stack up ofmanufacturing tolerances which could adversely impact the dose accuracy.

[0016] Still another advantage of the present invention is that amedication dispensing apparatus can be provided which can be primed evenafter having been cocked for injection, thereby avoiding any wasting ofmedication associated with having to uncock a cocked apparatus forpriming purposes.

[0017] Still another advantage of the present invention is that amedication dispensing apparatus can be provided in which even if itspriming mechanism is used after the apparatus is cocked for injection,the amount of medication to be delivered by operation of the cockedapparatus is not altered.

[0018] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided which can be primed bymanually and continuously rotating a priming sleeve as far as necessary,including one or more complete revolutions, which priming is highlyadjustable and does not waste a sizeable amount of medication.

[0019] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided with an uncomplicatedand compact design that contributes to a small axial profile anddiameter of the apparatus.

[0020] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided which is accurate, andsimpler in design and operation than many existing devices.

[0021] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided with a drive member thatcan be reset and a medication cartridge that can be replaced, therebyallowing the apparatus to be reused rather than discarded when itsinitial medication cartridge is spent.

[0022] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided with a drive member thatis automatically axially unlocked so as to allow reset when a medicationcartridge is being replaced.

[0023] Yet another advantage of the present invention is that amedication dispensing apparatus can be provided with a drive member thatduring the final stage of its axial reset is automatically shifted toits final position so as to provide feedback to the user that the drivemember has been reset properly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The above-mentioned and other advantages and objects of thisinvention, and the manner of attaining them, will become more apparent,and the invention itself will be better understood by reference to thefollowing description of embodiments of the invention taking inconjunction with the accompanying drawings, wherein:

[0025]FIG. 1 is a diagrammatic perspective view of a first embodiment ofa medication dispensing apparatus with pull/push to inject and rotate toprime mechanisms of the present invention;

[0026]FIG. 2 is an exploded perspective view of the medicationdispensing apparatus of FIG. 1;

[0027]FIG. 3 is an exploded cross-sectional view of portions of themedication dispensing apparatus of FIG. 2;

[0028]FIG. 4 is a perspective view of portions of the medicationdispensing apparatus of FIG. 1 during assembly;

[0029]FIG. 5 is a diagrammatic cross-sectional view of the proximalparts of the medication dispensing apparatus of FIG. 1 in a ready orready-to-be-cocked state;

[0030]FIG. 6 is a cross-sectional view conceptually similar to the viewof FIG. 5, but after the apparatus has been manipulated from itsready-to-be-cocked state to a cocked or ready-to-inject state;

[0031]FIG. 7 is a cross-sectional view taken along line 7-7 of FIG. 5;

[0032]FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 6;

[0033]FIG. 9 is a diagrammatic perspective view of another embodiment ofa medication dispensing apparatus with pull/push to inject and rotate toprime mechanisms of the present invention;

[0034]FIG. 10 is an exploded perspective view of the medicationdispensing apparatus of FIG. 9;

[0035]FIG. 11 is an exploded perspective view of portions of theapparatus of FIG. 10;

[0036]FIG. 12 is an exploded perspective view of other portions of theapparatus of FIG. 10;

[0037]FIG. 13 is a diagrammatic cross-sectional view of proximalportions of the medication dispensing apparatus of FIG. 9 in a ready orready-to-be-cocked state;

[0038]FIG. 14 is a cross-sectional view conceptually similar to the viewof FIG. 13, but taken along a cut-line oriented 90° relative thereto,and after the apparatus has been manipulated from its ready-to-be-cockedstate to a cocked or ready-to-inject state;

[0039]FIG. 15 is a cross-sectional view conceptually similar to the viewof FIG. 13, but after the cartridge assembly has been removed forinsertion of a replacement cartridge and the drive member has beenreset;

[0040]FIG. 16 is a diagrammatic front view in partial cross-section ofanother embodiment of a reusable injector pen of the present inventionwith an alternate means for resetting the drive screw;

[0041]FIG. 17 is a diagrammatic perspective view in cross-section ofrelevant portions of another embodiment of a reusable injector pen ofthe present invention with an alternate drive screw reset mechanism;

[0042]FIG. 18 is a diagrammatic, partial perspective view incross-section of a reusable injector pen of the present invention thatemploys an over-center spring mechanism to assist drive screw reset; and

[0043]FIG. 19 is a diagrammatic, partial perspective view incross-section of the injector pen of FIG. 18 after completion of thedrive screw reset.

[0044] Corresponding reference characters indicate corresponding partsthroughout the several views. Although the drawings representembodiments of the present invention, the drawings are not necessarilyto scale, and certain features may be exaggerated or omitted in some ofthe drawings in order to better illustrate and explain the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0045] Referring now to FIGS. 1 and 2, there is shown a first embodimentof a medication dispensing apparatus with rotate to prime and pull/pushto inject functionality of the present invention. The apparatus,generally designated 20, is shown in a form commonly known as aninjector pen, although other forms are within the scope of theinvention. Medication injector pen 20 is a disposable pen, in that afterthe quantity of medicine contained therein is exhausted by multipleoperations of the pen, the entire pen is discarded rather than beingreset and reloaded with a replacement container of medicine. Pen 20 isrepeatably operable to deliver into a user a fixed dose, i.e., a dose inan amount which is not settable by a user but which instead is in aspecific amount dictated by the pen manufacturer by virtue of theparticular design of the pen. While different injector pens, which areconceptually similar but slightly different in design, may be providedto allow for different fixed doses, each of such different pens is onlyadapted to repeatedly deliver a particular fixed dose.

[0046] Injector pen 20 includes a distal portion 22 with a distalneedled end and which contains the medicinal fluid to be delivered uponpen operation, and a proximal portion 24 which contains the injectingand priming mechanisms used to force the contained medicine from theneedled end. In the shown embodiment, distal portion 22 includes aretainer 28 and a cartridge 48 held therein. Cartridge retainer 28 ismade of transparent plastic and includes a distal end 30 and a proximalend 32. External threading 34 around retainer distal end 30, or othersuitable connection means, are used to releasably connect a pen-needleassembly generally designated 38.

[0047] Pen-needle assembly 38 is of known design and includes adouble-ended needle cannula or injection needle 40 having a distal tip42 at one end and a not-shown proximal point at the other. Injectionneedle 40 is mounted in a tubular hub 44 that is internally threaded tocooperate with the shown retainer design so as to be screwable onto andoff of threading 34 of retainer distal end 30. Although the needleassembly is shown as having a single injection needle, needle assemblieswhich may be used with the present invention may be of various typesknown in the art, including, but not limited to, assemblies with one ormore shortened injection needles, including microneedle arrays.

[0048] The proximal end 32 of cartridge retainer 28 includes an openingthat receives a glass cartridge 48, and after receiving the cartridgethe retainer proximal end 32 is fixedly mounted or secured, viaadhesives, ultrasonic welding or in another suitable manner, to apreviously subassembled pen proximal portion 24 when injector pen 20 isassembled by the manufacturer.

[0049] Cartridge 48 is of conventional design and defines amedicine-filled reservoir 50 which is closed at its proximal end by apiston 52 that is axially slidably and sealably engaged with thecartridge interior wall to hold the fluid medication within reservoir50. The distal, outlet end of cartridge reservoir 50 is sealed by aseptum 54 held by a cap 56 that is secured to a stepped-down diameterneck portion 49 of the cartridge. When pen-needle assembly 38 is mountedon the distal end of cartridge retainer 28 holding cartridge 48, theproximal point of injection needle 40 penetrates cartridge septum 54 toprovide a fluid flow outlet by which medicine within cartridge reservoir50 can be dispensed from needle tip 42 during operations of injector pen20.

[0050] The fluid medicine container shown and described above isillustrative and not intended to be limiting as other constructions maybe employed within the scope of the invention. For example, rather thanhaving a distinct cartridge held within a separate retainer as in theshown fluid container, a fluid container may be provided in the form ofan extension of the exterior housing of the pen into which areintegrated the cartridge features. In another fluid container embodimentof the invention, the cartridge could be constructed to be sufficientlydurable and adapted to secure directly to pen proximal portion 24without any protective retainer therearound, and with the pen-needleassembly directly mountable to the cartridge.

[0051] With additional reference to FIGS. 3-8, pen proximal portion 24of injector pen 20 consists of an external, protective housing 60, anaxially advanceable drive member 80, a rotatable driver 100, a follower140 and a plunger 160.

[0052] Housing 60 is injection molded as a single piece from a plasticmaterial such as polycarbonate, and has a cylindrical, tubular body 62with a distal end 64 and a proximal end 66. Distal end 64 is rigidlysecured with cartridge retainer 28 when injector pen 20 is assembled bythe manufacturer. Adjacent proximal end 66, the interior surface of body62 includes a series of axially-aligned ratchet teeth 68 which continueuninterrupted around the entire internal circumference of the proximalend of the housing body. As best shown in the cross-sectional view ofFIG. 7, ratchet teeth 68 have a one-way ramping so as to be engaged bythe one or more pawls 108 used to prevent rotation in one particulardirection relative to housing 60 of the pawl-mounting driver 100.Although ratchet teeth 68 number thirty-six in the shown embodiment,fewer or additional teeth which provide suitable anti-rotationcapabilities may be used.

[0053] Near distal end 64, housing body 62 includes at least one, andpreferably a pair of tabs 70, used to engage drive member 80 to preventits rotation relative to housing 60. As best shown in FIG. 8, tabs 70project radially inward from diametrically opposed regions of thehousing body interior surface, and include rectangular-shaped heads 72.Heads 72 jut proximally from tabs 70, and further extend to body 62 toserve as reinforcing ribs for tabs 70. Tab heads 72 fit within grooves90 of drive member 80.

[0054] On the body interior surface at an axial position betweenanti-rotation tabs 70 and proximal end 66 is a circumferentiallyextending shoulder 74 that juts radially inward approximately twice thedistance as the peaks of ratchet teeth 68. Shoulder 74 serves as alatching point for driver 100. Shoulder 74 is continuous around thehousing body internal circumference except for two sections whereratchet teeth 68 extend through toward anti-rotation tabs 70. These twosections are provided to facilitate a one-piece molding of the shownbody, and in embodiments where the shown housing is formed from multiplepieces, such as mating halves assembled together, these interruptions ofshoulder 74 may be eliminated.

[0055] Drive member 80 is in the form of a drive screw that is injectedmolded from plastic such as polycarbonate as a single-piece. Drive screw80 has a shaft 82 with external threading 84 along essentially itsentire axial length. Threading 84 is a single thread that is generallyright triangular in axial cross-section, with a flat edge alignedperpendicular to the axial direction and facing the proximal direction,and which spirals along the shaft 82 to create a helical pattern. Amultiple start thread alternatively may be used to create a suitablethreading.

[0056] The distal end of drive screw 80 includes a foot 86 that has alarger surface area than the transverse cross-sectional area of shaft 82to distribute loading on the cartridge piston 52 that foot 86 contactsand thereby directly engages during piston advancing. Two rectangularnotches 88 in the periphery of foot 86 are aligned with a pair ofdiametrically arranged and longitudinal grooves 90 formed in screw 80.Grooves 90, which have a squared-off shape and a smooth base, extend theentire axial length of shaft 82 and slidably accommodate anti-rotationtab heads 72 which permit translation of drive screw 80 relative tohousing 60. Foot notches 88 allow introduction of tab heads 72 intogrooves 90 during assembly by the manufacturer of the one-piece housing60 to the subassembly shown in FIG. 4, which shown subassembly resultsfrom screw 80 being screwed during assembly into a subassemblyconsisting of follower 140, plunger 160, and driver 100. While thenumber of grooves 90 preferably corresponds to the number ofanti-rotation tab heads 72 which may be fewer or greater in number, thenumber of such grooves and tabs is preferably limited to two as shown soas to ensure a durable, rotation preventing construction while creatingonly limited interruptions to the threading.

[0057] Priming driver 100 is injection molded from a resilient plasticmaterial such as ABS. Driver 100 includes a tubular, cylindrical gripportion 102 that at its distal end is stepped down to a tubular,cylindrical body portion 104, which is further stepped down to bodyportion 107. Grip portion 102 has an outer diameter that generallyconforms to the outer diameter of housing body 62 so as to blend intothe housing proximal end 66 to which it is adjacent. Grip portion 102 isthe part of driver 100 which is externally accessible to be manuallyrotated by a user for pen priming purposes. To faciliate being turned bycontact with one or more of a user's fingers during pen priming, gripportion 102 preferably is provided with an elastomeric ring 103 having ahigh coefficient of friction and which is fixedly secured, such as via afriction fit or possibly with adhesives, around the outer radialperiphery of the grip portion. Rather than the shown ring 103, gripenhancing features, such as radial protrusions integrally formedthereon, may be molded into grip portion 102, in which case driver 100may be entirely formed of a one-piece molded construction.

[0058] Driver body portion 104 extends distally from grip portion 102and is sized to insert within the interior hollow of housing body 62.Within a proximal region of body portion 104, at least one pawl isformed which cooperates with ratchet teeth 68 to limit the rotation ofdriver 100 relative to housing 60 to a single direction. In the showndriver 100, a pair of nearly diametrically opposed pawls are provided inthe form of angularly extending, radially bendable pawl fingers 106having catch ends 108 that extend sufficiently far radially outward toengage ratchet teeth 68. By slightly offsetting the pawls so as to notbe precisely diametrically opposed, as shown in FIG. 7, one catch end108 can engage a ratchet tooth 68 while the other catch end 108 is beingramped inward by contact with the middle of a different ratchet tooth68, whereby the angular precision of the offset pawls is twice as goodas if lined up diametrically. From the perspective of a FIG. 7 viewer,priming driver 100 can be rotated in a counter-clockwise directionrelative to housing 60 as pawl fingers 106 are forced to bend radiallyinward, and then snap radially outward, as catch ends 108 slide alongthe ramped surfaces of ratchet teeth 68, and then drop over the teethpeaks. Priming driver 100 is prevented from being rotated in a clockwisedirection relative to housing 60 by the engagement of one of the pawlcatch ends 108 with the radially-aligned stop face of a ratchet tooth68. This restriction on rotation not only ensures that a user willrevolve priming driver 100 in the proper direction to achieve penpriming, but also, due to the connection of the driver with the drivescrew described further below, prevents the drive screw from backing upor moving proximally which may result in an incorrect dose.

[0059] Body region 107 further includes a pair of raised portions 109.Raised portions 109 are diametrically opposed and are in closerproximity to ratchet ribs 68 than body region 107 so as to stabilizedriver 100 within housing 60.

[0060] The distal region of driver body portion 107 is divided by aplurality of slot-shaped notches 110 into two sets of axially extending,radially resilient fingers. The first set of fingers, generallydesignated 114, are used to assemble driver 100 to housing 60 andfollower 140 to driver 100, and are identically shaped. Fingers 114 arethree in number in injector pen 20 and are centered 120° apart. Eachfinger 114 includes a latching rib 116 and a stop rib 120. Each latchingrib 116 projects radially outwardly from an outer surface of itsrespective finger 114 near the distal end thereof. Each stop rib 120projects radially inwardly from an inner surface of its respectivefinger 114 at an axial location proximal of rib 116. The distal face ofeach rib 116 has a ramped or camming surface 118, and the proximal faceof each rib 120 has a camming surface 122.

[0061] Latching ribs 116 cooperate with the distal face of housingshoulder 74 to axially retain driver 100 within housing 60. Duringmanufacturing assembly, as the subassembly including driver 100 isinserted distally into housing 60 as shown in FIG. 4, the engagement ofall of the camming surfaces 118 with shoulder 74 bends the distal endsof fingers 114 inwardly so as to allow ribs 116 to pass over shoulder74, at which time fingers 114 snap outward due to their resilientconstruction, thereby latching ribs 116 to shoulder 74 to preventproximal withdrawal of driver 100. Ribs 116 are axially positioned suchthat when snapped into latching engagment with shoulder 74, the housingproximal end 66 is in closely spaced relationship with annular shoulder105 of grip portion 102, and further axial insertion in a distaldirection of driver 100 within housing 60 is prevented by the abutmentof shoulder 105 with the end of the housing.

[0062] The second set of fingers, generally designated 126, includeL-shaped extension portions 128 and are used to engage drive screw 80 toconvert driver rotation into drive screw axial motion. The base of eachof the three fingers 126 proximal of extension portions 128 is locatedbetween successive fingers 114, and fingers 126 are centered 120° apart.A stop tab 136 laterally projects from a central region of each offinger extension portions 128.

[0063] A projecting thread segment 132 is formed on a radial innersurface of each extension portion 128 and mates with external threading84 of drive screw 80. To completely mate with threading 84, each threadsegment 132 is positioned at a different axial position on itsrespective extension portion 128 such that the thread segments 132, butfor the interruptions resulting from the circumferential or angularspacing of extension portions 128, form part of a continuous helicalthread with the same pitch as threading 84 of screw 80. As further shownin FIG. 5 and 6, each thread segment 132 in axial cross-section has aramped proximal face 133 and a radially-aligned stop face 134. Theresilient construction of driver 100 allows extension portions 128 tosplay outward such that thread segments 132 can axially slide over screwthreading 84 when the drive screw is advanced during injecting asdescribed below. In particular, thread segments 132 slide along theramped thread face and then insert within the indentation formed by theradial drop off between the axial end of one pass of threading 84 andthe start of the adjacent pass of the threading.

[0064] While three of each of fingers 114 and 126 are shown, fewer oradditional fingers may be used within the scope of the invention. Forexample, as few as one finger with extension portion 128 may beprovided, although at least two are used to achieve a secure, directengagement with the drive screw threading 84. In addition, as fingers114, and thereby the base of fingers 126, result from notches 110 thatprovide flexibility for snap insertion of the driver into a one-piecehousing, and the follower into the driver, if a multiple piece housingwhich can be assembled around the priming driver is used, and thefollower were adapted to flex inward during assembly, fingers 114 andthe base of fingers 126 could be eliminated, and their featuresincorporated into a continuous sleeve.

[0065] Axially movable within the internal hollow of driver 100 is afollower, generally designated 140, which is injection molded as asingle piece from a resilient plastic material such as acetal. Follower140 includes a central annulus 142 with a proximal surface 144 thatabuts stop ribs 120 during pen cocking as described below. Duringmanufacturing assembly, as follower 140 is inserted distally into driver100, annulus 142 engages camming surfaces 122 to bend fingers 114outwardly so as to allow annulus 142 to pass over ribs 120, at whichpoint fingers 114 resiliently snap back inward to prevent proximalwithdrawal of follower 140.

[0066] At least one finger, and preferably two or more, such as thethree fingers 146 shown in injector pen 20, extend distally from theinner radial region of annulus 142 to engage drive screw 80. The threefingers 146 are generally rectangular in shape and centered 120° apart.Each finger 146 includes a distal end 147, and an inwardly projectingthread segment 148 formed on a radial inner surface. In the preferredembodiment, each thread segment 148 mates with external threading 84 ofdrive screw 80, and to fit properly therewith each thread segment 148 ispositioned at a different axial position on its respective finger 146 tobe aligned as separated pieces of a continuous helical thread. Asfurther shown in FIG. 5 and 6, each thread segment 148 in axialcross-section has a ramped proximal face 149 and a radially-aligneddrive face 150. The resilient construction of follower 140 allowsfingers 146 to splay outward as the follower is pulled proximally byplunger 160 during pen cocking as described below, such that threadsegments 148 can axially slide over the threading 84 of rotatably fixedscrew 80.

[0067] In injector pen 20, follower 140 uses its engagement with thescrew threading to force drive screw 80 axially during injecting asdescribed below. To maintain helical thread alignment between thefollower and screw and the driver and screw, the follower 140 is keyedto driver 100 to rotate therewith. This keying is achieved by eachfollower finger 146 closely fitting within the space between adjacentdriver finger extension portions 128. Driver 100 and follower 140 may besuitable keyed together in alternate manners in different embodiments,such as via a spline that fits within an added notch in annulus 142, ora pin and slot.

[0068] In another embodiment which is not shown, a follower does not actagainst the drive screw threading during injecting, but rather againstat least one rack of axially spaced teeth distinct from threading 84 andwhich extends longitudinally along the drive screw. In this design, thefollower does not rotate with driver 100, but rather is rotationallyfixed to the drive screw. One suitable rack for this alternate designuses a pair of racks, one formed within each groove 90, and theresilient follower fingers are two diametrically opposed fingers thatinclude transversely extending teeth rather than the projecting threadsegments 148 so as to mesh with the racks.

[0069] A plurality of mounting fingers 152, such as the four shown,extend proximally from the inner radial region of annulus 142. Latches154 jut radially outwardly from the proximal ends of fingers 152.

[0070] Plunger 160 is injection molded from a lightweight material suchas polycarbonate. Although shown as having a one-piece construction, tofacilitate manufacture plunger 160 is formed of multiple parts assembledtogether, such as a tubular main body with a cap over the proximal endof the main body. Plunger 160 includes a grip portion 162 extendingdistally of driver 100 which is externally accessible to be manuallypulled by a user for pen cocking purposes. Along its length in theproximal direction, grip portion 162 is radially outwardly flared so asto be more readily grasped by user, such as between the thumb andfingers of a user, when pulled to the left from the perspective of aviewer of FIG. 1. Other graspable grip portion configurations may besubstituted, such as a loop in which a finger can insert, or a bar underwhich fingers can be looped. The proximal end 164 of plunger 160 servesas a push surface against which a force can be applied to push theplunger of a cocked pen to the right from the perspective of a viewer ofFIG. 1.

[0071] The distal end of grip portion 162 is stepped down to acylindrical tube portion 166 that fits within the interior hollow ofdriver 100 and is slidable into and out from such hollow during use ofpen 20. An inward lip 168 is formed at the distal end of tube portion166, and four circumferentially spaced bars 170 axially project from thelip and support a plunger ring portion 172 including a frustroconicalinner surface 174. The space between ring portion 172 and lip 168defines a recess or groove 176 around the inner circumference of plunger160 and inward of bars 170 which in injector pen 20 is used to connectplunger 160 with follower 140 so as to be axially fixed but rotatablyfree or free wheeling.

[0072] During manufacturing assembly, as follower 140 is insertedproximally into plunger 160, the engagement of latches 154 by innersurface 174 bends the proximal ends of mounting fingers 152 inwardlyuntil latches 154 pass inner surface 174, at which time fingers 152 snapoutward due to their resilient construction, thereby inserting latches154 within groove 176 and latching the proximal face of ring portion 172to prevent distal withdrawal of follower 140 as plunger 160 is movedproximally. The proximal face of latches 154 abuts inward lip 168 toprevent over insertion of follower 140, and to cause axial motion ofplunger member 160 in a distal direction to axially move follower 140distally. Latches 154 are slidable within groove 176 such that rotationof follower 140 does not necessarily cause rotation of plunger 160, andvice versa.

[0073] The structure of injector pen 20 will be further understood inview of the following explanation of its operation given with primaryreference to FIGS. 5 and 6. Initially, a user requiring a dose ofmedication will locate pen 20, which normally will be in the readyarrangement shown in FIG. 5, which is the arrangement in which the penremained after its previous use, or in which the pen is provided to auser for its first use.

[0074] Pen 20 is first primed. Typically while clutching the housing 60and/or distal portion 22 in one hand while pointing the needle tip 42upward, a user grips driver grip portion 102 using one or more digits ofher other hand, with slippage limited by ring 103, and begins tomanually rotate it and thereby all of the rest of priming driver 100relative to housing 60. Driver 100 can only be rotated within thehousing in one direction, as the engagement of the pawl teeth 108 withratchet teeth 68 prevent rotation in the opposite direction. Therotation of finger extension portions 128 during driver rotation causesdrive screw 80, due to it being rotationally fixed relative to thehousing 60 by tab heads 72, to axially translate in the distaldirection, or to the right in FIG. 5. In particular, because threadsegments 132 engage threading 84 of drive screw 80, as thread segments132 are rotated, due to the screw being rotatably fixed and driver 100being prevented from axially moving within the housing in the proximaldirection by the latching of ribs 116 with housing shoulder 74, screw 80is forced to translate distally. As drive screw 80 translates distally,the cartridge piston 52 which is not shown in FIGS. 5 and 6 is pusheddistally by foot 86, thereby decreasing the reservoir volume for themedication in the cartridge such that medication is forced toward needletip 42. Normally, foot 86 will be in contact with piston 52 at the startof the priming, but rotation of the priming driver, before causingpiston 52 to move, will naturally close up any gap between foot 86 andpiston 52, such as most likely to exist during the first ever use of pen20. Driver 100 is able to be continuously rotated by a user duringpriming, whether it be through a fraction of a revolution, or one ormore revolutions, until the user sees that the piston movement hascaused medicine to reach the upward pointed needle tip 42 as all air isexpelled, at which time the user stops twisting driver 100 as priming iscomplete.

[0075] During pen priming, follower 140 rotates with driver 100 due toits keying together, but because of the free wheeling connection ofplunger 160 with follower 140, plunger 160 does not have to rotate aswell, and therefore any restriction on twisting of the plunger does nothinder priming.

[0076] After priming, pen 20 is ready to be used for injection. Apulling step is first performed to cock or prepare the uncocked pen 20to deliver the dose for which it has been designed. During that pullingstep, and again while housing 60 and/or distal portion 22 is grasped inone hand, a user uses her other hand to pull plunger grip portion 162axially away from driver 100 and housing 60. Plunger grip portion 162 ispulled proximally a fixed distance, specifically until shoulder 144 offollower 140, which is also being pulled rearward due to its connectionwith the plunger, abuts stop ribs 120, which abutment halts the axialmovement of plunger 160. During this follower movement, the distal endsof fingers 146 first flex or bend radially outward as the rampedproximal faces 149 of thread segments 148 slide up the ramped distalface of the threading 84, and then snap back inward as thread segments148 slip over the peaks of the thread. In injector pen 20, the distancethe follower axially moves is only slightly greater than the pitch ofthreading 84, such that each thread segment 148 only slides overthreading 84 once during a pen cocking, which threading, along an axialcross-section of the drive screw serves as a series of axially spacedprojections for engagement with the finger thread segments. In alternateembodiments, follower 140 can be adapted to slide past multiple threadpasses or projections during its retraction. As follower thread segments148 slide over threading 84, drive screw 80 is prevented from beingpulled proximally by the abutment of threading 84 with stop faces 134 ofthe driver thread segments 132. In addition to the tactile signalresulting from the follower annulus 142 bumping against driver rib 120,the completion of the withdrawal stroke of plunger 160 may be indicatedin other ways, such as is disclosed in U.S. patent application Ser. No.60/279070 entitled “MEDICATION DISPENSING APPARATUS CONFIGURED FOR PULLTO SET DOSE AND PUSH TO INJECT SET DOSE FUNCTIONALITY,” the entiredisclosure of which is incorporated herein by reference.

[0077] At this point in time, pen 20 has been cocked or prepared todeliver the medicine dose it was designed to inject, and is arranged inthe ready-to-inject state shown in FIG. 6. If a user has not previouslyprimed pen 20, or has forgotten that priming has been performed, due tothe fact that driver thread segments 132 always engage drive screwthreading 84, driver grip portion 102 can still be twisted to causepriming of the pen without moving the pen from its cocked state.Advantageously, such priming does not alter the volume of medicine to bedelivered by subsequent plunging of the cocked plunger 160.

[0078] To actually inject the medicine, after pen 20 is manipulated sothe injection needle distal tip 42 properly penetrates a user's skin, orother injection site, an axial, distal plunging force is applied to pushsurface 164 to force plunger 160 distally. As follower 140 is moveddistally by plunger 160, the abutment of drive screw threading 84 bydrive faces 150 of thread segments 148 causes drive screw 80 totranslate distally to shift piston 52 and force medication throughneedle 40. In particular, the pitch of screw threading 84 is selectedsuch that the force necessary to advance piston 52 within cartridge 48is less than the input force that would be required to overcome theforce of friction between thread segments 148 and threading 84, andtherefore screw 80 is advanced instead of follower 140 being rotated.During this drive screw advancement, the distal ends of finger extensionportions 128 flex or bend radially outward as the ramped faces 133 ofthread segments 132 slide up the ramped distal face of the passingthreading 84, and then snap back inward as the peaks of the threadingpass thread segments 132. Plunging motion of plunger 160, and therebyadvancement of drive screw 80, is stopped, and the medicine injection iscomplete, when the distal ends 147 of all the follower fingers 146simultaneously abut stop tabs 136 of finger extension portions 128.

[0079] Pen 20 can continue to be used to deliver its fixed dose untilthe medicine remaining in the cartridge is insufficient for a properdosing, which insufficiency may be indicated to a user by her inabilityto fully withdraw the plunger to cock the apparatus due to, for example,the follower engaging a not shown stop associated with the drive screw.When insufficient medicine remains, pen 20 is to be disposed of andreplaced with a similar but entirely new pen.

[0080] Referring now to FIGS. 9-15, there is shown another embodiment ofa medication dispensing apparatus with rotate to prime and pull/push toinject functionality of the present invention. The apparatus, generallydesignated 220, serves as a reusable injector pen, in that after thequantity of medicine contained in a cartridge therein is exhausted bymultiple operations of the pen, the cartridge can be removed andreplaced with a full cartridge, and the pen otherwise reset, to be usedagain. As with injector pen 20, pen 220 is operable to deliver into auser a particular fixed dose per each use. As will be recognized by theskilled artisan, the designs of injector pen 220 and pen 20 are in manyrespects similar, and therefore not only are similar parts of injectorpen 220 not all exhaustively detailed below, but also certain parts ofinjector pen 20 could be correspondingly modified.

[0081] The distal portion of injector pen 220 includes a one-pieceretainer 222 and a medication cartridge 238 held therein. Cartridge 238is identical to cartridge 48 and includes a medicine-filled reservoir240 and a slidable piston 242. Cartridge retainer 222 is made of anopaque plastic but includes two windows 223 through which the cartridgecontents are visible. External threading 225 around the retainer distalend 226 is used to releasably connect a pen-needle assembly 230,identical to pen-needle assembly 38, such that the proximal point of theinjection needle of assembly 230 penetrates the cartridge septum toprovide a fluid flow outlet by which medicine within cartridge reservoir240 can be dispensed during injector pen use.

[0082] A collar portion 227 at the proximal end of cartridge retainer222 includes a central opening through which a cartridge 238 is loadedand unloaded. A series of detents 228 on the exterior surface of collarportion 227 allow for the snap fit attachment of a not shown pen cap viaa mating indent or groove in that cap. Collar portion 227 includes ameans for removably mounting retainer 222 to the housing of the proximalportion of injector pen 220. Such means are shown as an internalthreading 229 that connects to an external threading 257 of housingouter shell 250. Other suitable forms of removably mounting theretainer, such as via a bayonet type connection or other connectionsystems known in the art, may be substituted within the scope of theinvention.

[0083] The form of removably mountable fluid medicine container shown inthe embodiment of FIGS. 9-15, which uses a disposable cartridge and areusable retainer, is merely illustrative and not limiting. Other formsof fluid containers, including but not limited to a fluid containercomprising a disposable retainer and a disposable cartridge, whichretainer is fixedly attached to the cartridge so as to be disposed oftogether, and where that fluid container is replaced as a combinationfresh cartridge/retainer, may be employed within the scope of theinvention.

[0084] The proximal portion of injector pen 220 includes a multi-parthousing formed of the outer shell 250, and a pair of inner shell halves251 and 252, each made from a plastic material such as polycarbonate.Shell halves 251 and 252 are identical in injector pen 220, andtherefore further description of shell half 251 has equal application toshell half 252. Shell halves 251 and 252 need not be identical tofunction properly.

[0085] The multi-part housing construction facilitates pen manufacture,as during manufacture inner shell halves 251 and 252 are securedtogether around the priming driver 280 described further below andfixedly secured within and to outer shell 250, for example with adhesiveapplied along glue groove 261 of the shell halves or with other suitablefasteners. This fixed securement results in shell halves 251, 252 beingaxially and rotatably fixed in outer shell 250. Shell halves 251 and 252are designed to contact each other on both angular ends when securedtogether around the driver.

[0086] Outer shell 250 has a tubular body 254 with a proximal end 255and a distal end portion 256 which is stepped down in diameter andexternally threaded at 257 to removably mount cartridge retainer 222.Near distal end portion 256, the interior surface of housing body 254includes a pair of diametrically opposed, radially inwardly projectingtabs 259 (see FIG. 14) used to engage the drive screw to prevent itsrotation relative to housing 250.

[0087] The interior surfaces of shell halves 251 and 252 define a seriesof axially-aligned ratchet teeth 263. In a finally assembled injectorpen 220, teeth 263 continue uninterrupted around the entire internalcircumference of the pen housing. Ratchet teeth 263 have a one-wayramping so as to be engaged by the one or more pawls 288 used to preventrotation in one particular direction of the pawl-mounting driver 280relative to the pen housing.

[0088] The axially advanceable drive member in injector pen 220 is adrive screw that includes a drive screw shaft 270 and a screw head 272,each injected molded from plastic such as polycarbonate. Drive screwshaft 270 has external threading 274 along essentially its entire axiallength. Threading 274 is a single thread that is generally righttriangular in axial cross-section, with a flat edge alignedperpendicular to the axial direction and facing the proximal direction,and which spirals along the shaft 270 to create a helical pattern. Apair of diametrically arranged and longitudinal grooves 276 formed inshaft 270 have a squared-off shape and a smooth base, and extendessentially the entire axial length of shaft 270 to sidably accommodateanti-rotation tabs 259 that permit translation of the drive screwrelative to the pen housing. Drive screw head 272 snap fits in aconventional manner onto a lipped nub 271 at the distal end of drivescrew shaft 270. Screw head 272 distributes loading on the cartridgepiston 242. The proximal end of drive screw shaft 270 includes aradially protruding head 278 that serves as an insufficient remainingdose stop as described further below.

[0089] The priming driver, generally designated 280, is injection moldedfrom a resilient plastic material such as ABS. Driver 280 includes atubular, cylindrical grip portion 282 that at its distal end is steppeddown to a tubular, cylindrical body portion 284. Grip portion 282 has anouter diameter that generally conforms to the outer diameter of housingouter shell 250 so as to blend into the housing end 255 to which it isadjacent. An elastomeric or O-type ring 285 fits tightly so as to benon-rotatable within a circumferential groove in grip portion 282.O-ring 285 makes it easier for a user to grip the driver, and furtherimproves the aesthetics. Grip portion 282 and its grip ring 285 is thepart of driver 280 which is externally accessible to be manually rotatedby a user for pen priming purposes.

[0090] Driver body portion 284 extends distally from grip portion 282and is sized to insert within the interior hollow formed by inner shellhalves 251 and 252. A pair of nearly diametrically opposed pawls areprovided in the form of angularly extending, radially bendable pawlfingers 288 having catch ends 289 that extend sufficiently far radiallyoutward to engage ratchet teeth 263 to limit the rotation of driver 280relative to shell halves 251, 252 to a single direction. In particular,priming driver 280 can be rotated in a first direction relative to thepen housing as pawl fingers 288 are forced to bend radially inward, andthen snap radially outward, as catch ends 289 slide along the rampedsurfaces of ratchet teeth 263, and then drop over the teeth peaks.Priming driver 280 is prevented from being rotated in the directionopposite to the first direction relative to the pen housing of injectorpen 220 by the engagement of one of the pawl catch ends 289 with theradially-aligned stop face of a ratchet tooth 263.

[0091] The distal region of driver body portion 284 is divided by aplurality of slot-shaped notches into two sets of axially extending,radially resilient fingers. The first set of fingers, generallydesignated 293, are identically shaped and used to assemble driver 280to the pen housing, as well as follower 320 to driver 280. Fingers 293are two in number and centered 180° apart. Each finger 293 includes amounting rib 296 and a stop rib 298. Each mounting rib 296 projectsradially outwardly from an outer surface of its respective finger 294near the distal end thereof. Each stop rib 298 projects radiallyinwardly from an inner surface of its respective finger 294 at an axiallocation proximal of rib 296.

[0092] Mounting ribs 296 fit into and slide within groove 265 of shellhalves 251, 252 arranged around the driver 280. When shell halves 251,252 are secured within housing 250, the interfitting of ribs 296 withingroove 265 results in driver 280 being axially fixed but rotatable inhousing 250.

[0093] The second set of fingers, generally designated 300, is used toengage drive screw shaft 270 to convert driver rotation into drive screwaxial motion. In injector pen 220, each finger 300 includes a base 302,a stepped portion 304, a cammable portion 306 and a tip portion 308.Base 302 of each of the two fingers 300 is located between successivefingers 293, and fingers 300 are centered 180° apart. A projectingthread segment 310 is formed on a radial inner surface of each tipportion 308 and mates with external threading 274 of drive screw shaft270. Each thread segment 310 is positioned at a different axial positionon its respective tip portion 308 such that the thread segments 310, butfor the interruptions resulting from the circumferential spacing of tipportions 308, form part of a continuous helical thread with the samepitch as screw threading 274. Each thread segment 310 in axialcross-section has a ramped proximal face and a radially aligned stopface. The resilient construction of driver 280 allows fingers 300 tosplay outward such that thread segments 310 can axially slide over screwthreading 274 when the drive screw is advanced during injecting.

[0094] Axially movable within the internal hollow of driver 280 is thefollower, generally designated 320, which is injection molded as asingle piece from a resilient plastic material such as acetal. Follower320 includes a tubular, cylindrical base 322 with two slots 324 spaced180° apart formed in its proximal end. A pair of stop ribs 328 and 330that limit the extent of plunger motion during pen use radially projectfrom base 322. Stop rib 328 is an annulus and completely rings base 322,and stop rib 330 is continuous except for interruptions at slots 324.During manufacturing assembly, as follower 320 is inserted distally intodriver 280, a ramped, distal face portion 329 of stop rib 328 engagesdriver stop ribs 298 to bend fingers 293 outwardly so as to allow stoprib 328 to pass over driver stop ribs 298, at which point fingers 293resiliently snap back inward to prevent proximal withdrawal of follower320.

[0095] An annular flange 333 at the distal end of base 322 defines acentral aperture 334 into which radially project a pair of diametricallyopposed stops 336. The space within the central aperture 334 betweenstops 336 is large enough to accommodate drive screw shaft 270, but isnot large enough to allow passage of stop head 278 at the proximal endof screw shaft 270. The abutting contact of the stops 336 by the shafthead 278 serves as an insufficient remaining dose indicator of injectorpen 220.

[0096] Axially projecting from annular flange 333 is a pair of fingers,generally designated 338, which are centered 180° apart. Each finger 338includes an upstanding base portion 340, a cammable portion 342 and atip portion 344. Each tip portion 344 includes an inwardly projectingthread segment 346 formed on a radial inner surface and which mates withexternal threading 274 of drive screw shaft 270. Each thread segment 346is positioned at a different axial position on its respective tipportion 344 to be aligned as separated pieces of a continuous helicalthread. Each thread segment 346 in axial cross-section has a rampedproximal face and a radially-aligned drive face, and the resilientconstruction of follower 320 allows fingers 338 to splay outward as thefollower is pulled proximally by plunger 360 during pen cocking asdescribed below, such that thread segments 346 can axially slide overthreading 274 of the rotatably fixed drive screw shaft 270.

[0097] Follower 320 uses its engagement with screw threading 274 toforce the drive screw shaft 270 axially during injecting. Follower 320is keyed to driver 280 to rotate therewith. In injector pen 220, thiskeying is achieved by each follower finger tip portion 344 closelyfitting within the space between adjacent driver finger tip portions308. In particular, tip portions 344 are dimensioned in conjunction withtip portions 308 such that when the pen injector is in the steady statearrangement shown in FIG. 13, the angular end faces of tip portions 344and 308 are in contact. This contact helps prevent any twisting of theflex fingers while in this steady state.

[0098] The angular dimensions of base portions 340 and cammable portions342 of the follower fingers 338, as well as the angular dimensions ofthe stepped portions 304 and cammable portions 306 of the driver fingers300, are selected so as to define a slot between adjacent fingers 300and 338 to accommodate the connecting arms of the wedge describedfurther below.

[0099] The slots 324 of follower base 322 result in the proximal regionsof base 322 serving as a pair of mounting fingers 325 that extendproximally toward plunger 360. A latching rib 350 juts radially outwardfrom the proximal ends of each of mounting fingers 325.

[0100] A plunger, generally designated 360, is injection molded in twoparts from a lightweight material such as polycarbonate. The plungerincludes a tubular main body 361 and a cap 362 that friction fits overthe proximate end of the main body. Plunger main body 361 includes agrip portion 364 extending distally of driver 280 which is externallyaccessible to be manually pulled by a user for pen cocking purposes.Along its length in the proximal direction, grip portion 364 is radiallyoutwardly flared so as to be more readily grasped by user, such asbetween the thumb and fingers of a user, when pulled to the left fromthe perspective of a viewer of FIG. 9. Other graspable grip portionconfigurations may be substituted. The proximal end of plunger 360formed by cap 362 serves as a push surface against which a force can beapplied to push the plunger of a cocked pen to the right from theperspective of a viewer of FIG. 9.

[0101] The distal end of grip portion 364 is stepped down to cylindricaltube portions 366 and 368 that fit within the interior hollow of driver280 and are slidable into and out from such hollow during use of pen220. An inward lip 370 is formed at the distal end of tube portion 368,and four circumferentially spaced bars 372 axially project from the lipand support a plunger ring portion 374 including an interrupted,frustroconical inner surface 376. The space between ring portion 374 andlip 370 defines a recess or groove 378 around the inner circumference ofplunger 360 and inward of bars 372, which groove 378 is used to connectplunger 360 with follower 320 so as to be axially fixed but rotatablyfree or free wheeling.

[0102] During manufacturing assembly, as follower 320 is insertedproximally into plunger 360, the engagement of latching rib 350 by innersurface 376 bends mounting fingers 325 inwardly until latching ribs 350pass inner surface 376, at which time fingers 325 snap outward due totheir resilient construction, thereby inserting latching ribs 350 withingroove 378 and latching the proximal face of ring portion 374 to preventdistal withdrawal of follower 320 as plunger 360 is moved proximally.The proximal face of latching ribs 350 abut inward lip 370 to preventover insertion of follower 320, and to cause axial motion of plungermember 360 in a distal direction to axially move follower 320 distally.

[0103] Extending within plunger 360 is a plastic stabilizing sleeve 353.Sleeve 353 may be provided to aid in preventing screw shaft 270 fromradially deflecting. Sleeve 353 is shown pressfit within a collar 380formed in cap 362, but alternatively could be mounted to follower 320.

[0104] In injector pen 220, the mechanism used to reset the drive screwwhen replacing a spent cartridge includes a wedge or camming element385, a biasing member 387, and an interfacing element 389, all housedwithin pen housing 250. This mechanism, when the cartridge is removed,automatically without manual operation thereon by the user, disengagesthe threaded engagement that existed between the drive screw shaft andboth the follower and driver, allowing the drive screw to be shiftedproximally.

[0105] Wedge 385 includes a circular camming ring 391 with a centralaperture 393 through which extends drive screw shaft 270. Camming ring391 fits within the space between the drive screw shaft 270 and both thedriver fingers 300 and the follower fingers 338. Camming ring 391 issized sufficiently small to slide axially without contacting driverstepped portions 304 or follower base portions 340. Camming ring 391 isalso sized sufficiently large to directly engage the internal conedsurfaces of driver cammable portions 306 and follower cammable portions342 when wedge 385 is slid distally from the position shown in FIG. 13,which engagement cams tip portions 308 and 344 radially outward so as todisengage thread segments 310 and 346 from drive screw threading 274.

[0106] Wedge 385 has four L-shaped connecting arms 395 that span cammingring 391 and a larger diameter, more distally located, circular outerring 397. During axial motion of wedge 385, each connecting arm 395slides within the slot formed between an adjacent driver stepped portion304 and follower base portion 340. Outer ring 397 encircles and is in aspaced relationship with driver fingers 300 and follower fingers 338.The outer periphery of ring 397 is closely spaced with the pen housingshell 250 to promote concentricity with the housing.

[0107] Biasing member 387 serves to force wedge 385 axially toward aposition at which the wedge cams outward the follower and driver fingersto disengage the drive screw. Biasing member 387 is shown as a coiledmetal compression spring having a first end that abuts the underside ofouter ring 397 radially outward of connecting arms 395, and an oppositeend that abuts an acetal washer 399 that is seated on the end faces ofshell inner halves 251, 252. Other known types of biasing members andmaterials of construction may be substituted for this metal compressionspring. Washer 399 better enables spring 387 to rotate with wedge 385,which wedge is forced to rotate with driver 280 and follower 320 due tothe capture of its connecting arms 395 therebetween.

[0108] Interfacing element 389 operably connects wedge 385 with themounted fluid container, and in particular cartridge 238 in the shownconfiguration of injector pen 220. Interfacing element 389 includes acollar portion 400 from which depends a pair of legs 402. Each leg isbowed outward or arcuate in transverse cross section and includes aradially protruding abutment rib 404 and an axially protruding alignmentrib 406 at its proximal end. When injector pen 220 is assembled, ribs406 fit within the central opening of wedge outer ring 397 to aid inconcentrically locating element 389 with wedge 385, and abutment ribs404 contact the distal surface of outer ring 397 to transfer to wedge385 force that is applied in the proximal direction on interfacingelement 389. Ribs 408 that extend longitudinally at both sides of eachleg 402 increase the strength of the legs.

[0109] Collar portion 400 includes a radially projecting annular flange410 that centers interfacing element 389 within the internal volume ofouter housing 250, as well as results in only a very small radial gapbetween the housing and the interfacing element. The distal face ofcollar portion 400 is stepped down and has a chamfered surface 412 and acartridge-abutting surface 414. Chamfered surface 412 aids in locatingthe proximal end of cartridge 238 on surface 414 when injector pen 220is assembled for use. Interfacing element 389 is prevented from fallingout of housing 250 when no cartridge is present by its engagement withother parts of the pen, such as portions of the housing. For example,the interfacing element may include one or more not shown, one-way snapsthat fit over and axially lock under anti-rotation tabs 259 duringmanufacturing insertion, which snaps, while not preventing proximalinsertion, prevent the distal withdrawal of interfacing element 389 frompen housing 250 due to the abutting engagement of the snaps with theunderside of tabs 259.

[0110] The structure of injector pen 220 will be further understood inview of the following explanation of its operation given with primaryreference to FIGS. 13-15. Initially, a user requiring a dose ofmedication will locate an injector pen 220 in the ready arrangementshown in FIG. 13.

[0111] Pen 220 is first primed in the same general manner as describedabove with respect to injector pen 20. After priming, pen 220 is stillarranged as shown in FIG. 13 and is ready to be used for injection. Bygripping grip portion 364, a user pulls plunger 360 axially away fromdriver 280 to cock the injector pen to deliver the dose for which it hasbeen designed. The proximal motion of the plunger 360 is halted when theunderside of follower stop rib 328, which follower is also being pulledproximally due to its connection with the plunger, abuts stop rib 298 ofdriver 280. During this plunger/follower proximal movement, the tipportions of follower fingers 338 flex out and slide over a thread ofexternal threading 274. During plunger/follower proximal motion, theengagement of threading 274 with the threads 310 of driver fingers 300prevent drive screw shaft 270 from being pulled proximally. At thispoint in time, pen 220 has been cocked or prepared to deliver themedicine dose it was designed to inject, and is arranged in theready-to-inject state shown in FIG. 14.

[0112] To actually inject the medicine, after pen 220 is manipulated sothe injection needle properly penetrates a user's skin, an axial, distalplunging force is applied to cap 362 to force plunger 360, and thereforefollower 320, distally. As follower 320 is moved distally by plunger360, the abutment of drive screw threading 274 by thread segments 346causes drive screw shaft 270 to translate distally to shift cartridgepiston 242 and force medication through the pen needle. During thisdrive screw advancement, driver tip portions 308 flex outward and slideover the passing threading 274. Plunging motion of plunger 360, andthereby advancement of drive screw shaft 270, is stopped, and themedicine injection is complete, when the distal face of follower stoprib 330 directly abuts the underside of driver stop rib 298.

[0113] Pen 220 can continue to be used in the above-described manner todeliver its fixed dose until the medicine remaining in the cartridge isinsufficient for a proper dosing. This insufficiency is indicated to auser by his or her inability to pull out the plunger sufficiently tocock the injector pen 220. Specifically, as plunger 360 is withdrawnproximally, follower stops 336 directly abut head 278 of drive screwshaft 270, which abutment prevents the follower thread segments 346 fromentirely passing over a thread, such that when the plunger withdrawingforce is removed, plunger 360 is typically drawn back into the penhousing to the ready state position shown in FIG. 13 by the resilientreturn of the follower fingers.

[0114] When only an insufficient dose remains, the user is able to swapout the cartridge 238 and reset the injector pen 220. Specifically,cartridge retainer 222 can be screwed off such that the cartridge andcartridge retainer are dismounted from outer shell 250, and thecartridge removed from the retainer and discarded. When cartridge 238 isso dismounted, coiled spring 387 forces wedge 385 and interfacingelement 389 distally. As wedge 385 moves distally, it encounters thecammable portions 306 and 342 of the driver and follower so as to splayoutward the tip portions 308 and 344. When the tip portions are sosplayed out, their respective thread segments are no longer engaged withthreading 274 of drive screw shaft 270, and the drive screw can beshifted proximally until the proximal face of head 278 abuts a not shownbottom stop, such as a hollow cylindrical protrusion, provided on theinterior surface of plunger cap 362.

[0115] To shift the drive screw proximally, the user can then, forexample, manually push back the extended drive screw 270 into theproximal portion of injector pen 220 with her finger. However, becausethe central hole in collar portion 400 of interfacing element 389 issmaller than the average finger, the user's finger may eventually startpushing interfacing element 389 down along with screw 270. And, when theinterfacing element and thereby the camming element 385 is so pusheddown a small amount, the camming outward of the flex fingers of thedriver and follower ceases and the thread segments reengage with thedrive screw threading 274, which reengagement may prevent the drivescrew 270 from completely resetting with its head 278 against the bottomstop. Therefore, to assure a complete reset, the user may resort tousing a tool, such as a pencil or perhaps a dedicated tool provided withpen 220, which fits through and does not move the interfacing element asit is used to push back the drive screw.

[0116] To ensure a complete resetting of the drive screw withoutpossibly requiring the use of a separate, external tool, the drive screwreset mechanism of the pen injector may employ an additional springdevice to urge the drive screw proximally. One such device is abstractlyshown in FIGS. 18 and 19, and is used in an injector pen 500 identicalto injector pen 220 except for the modifications described below. Thedevice employs at least one, and preferably two, over-centerspring-loaded assemblies, generally designated 502, that work with arecess provided in the drive screw. Each assembly 502 includes a shownpivotable member 504 and a not shown biasing member that tends to forcepivotable member 504 toward the arrangement shown in FIG. 19. Thebiasing member, which may be a known type of spring such as a torsionalspring or a leaf spring, acts between member 504 and the pen housing.Pivotable member 504 has a fork portion 505 that is pivotally mounted totwo not-shown projecting ears formed in shell 250 on either side of forkportion 505, and a finger portion 506 that projects from fork portion505 and fits within a groove 276 of drive screw shaft 270. The tip offinger portion 506 is dimensioned to act against a ledge 507 formed by arecess in the screw, which in the shown embodiment is fashioned by athroughbore 508 connecting grooves 276. During use of injector pen 500,the tips of finger portions 506 slide along groove 276. When a cartridgeis removed for replacement, and the follower and driver flex fingers areautomatically splayed outward and the drive screw is started to bemanually pushed back during reset in preparation for loading a newcartridge to pen 500, which stage of the reset is shown in FIG. 18,over-center spring loaded assemblies 502 do not interfere with or assistreset. However, when drive screw reset reaches a certain point butbefore the interfacing element will be pushed downward, such as when thedrive screw is approximately six millimeters from the bottom of itsdesired travel, the tips of finger portions 506 insert within bore 508and act proximally against the screw ledge 507, and the not shownbiasing members serve to automatically snap pivot members 504 down tothe arrangement shown in FIG. 19 to finish the downward travel of thedrive screw for the user such that the drive screw 270 completely resetswith its head against the bottom stop. Over-center spring loadedassemblies 502 thereby insure the drive screw reaches its bottomposition, as well as provide a positive feedback that the drive screwhas been reset properly.

[0117] In other embodiments, different elements to help ensure acomplete resetting of the drive screw may be employed. Such elementsinclude a constant force spring attached between the plunger cap and thedrive screw proximal end, or a clip spring mounted to the interior ofthe plunger cap and which is shaped to grab and pull proximally thedrive screw when the drive screw head 278 is inserted therein duringscrew reset.

[0118] After drive screw reset, the proximal portion of injector pen 220is arranged as shown in FIG. 15.

[0119] After a new replacement cartridge 238 is inserted into cartridgeretainer 222, remounting the cartridge assembly to the pen housingresults in the cartridge abutting the interfacing element 389 to forceit proximally, which in turn forces wedge 385 proximally against thereturning force provided by spring 387. It will be appreciated that ifpen 220 includes a reset assisting device such as shown in FIGS. 18 and19, this remounting can be used to reset the drive screw instead of thedrive screw being pushed back with a user's finger, as the drive screwcan be pushed back by contact with the cartridge piston as a newcartridge loaded within retainer 222 is removably mounted to shell 250during reassembly of pen 220.

[0120] As wedge 385 moves proximally, the camming outward of the flexfingers of the driver and follower ceases and the thread segmentsreengage with the drive screw threading 274. After the cartridgeassembly remounting, injector pen 220 can then be primed and used in themanner previously described until another new cartridge is needed, atwhich time the process is repeated.

[0121] It will be appreciated by the skilled artisan that injector pen220 can be manufactured as a disposable pen merely by fixedly mounting,as opposed to removably mounting, the cartridge retainer with loadedcartridge to the pen housing. In such a disposable embodiment, theinterface 389, wedge 385 and spring 387 may be eliminated as drive screwreset is not necessary.

[0122] While the mechanism shown being used in injector pen 220 to resetthe drive screw is preferred, other mechanisms for resetting the drivescrew may be substituted in alternate reusable devices of the presentinvention. For example, and as diagrammatically shown in FIG. 16,injector pen 430 includes the same working components as injector pen220, except that it lacks wedge 385, biasing member 387 and interfacingelement 389. Instead, the reset mechanism of injector pen 430 includesan externally accessible, slidable collar with an internal portion thatengages cammable arms added to the drive screw engaging fingers of thedriver and follower. The collar is formed in one piece with an annulargrip portion 432 that is disposed around the pen housing, an annularflange 434 that resides within the pen housing internal volume, andcircumferentially spaced bridges 436 spanning grip portion 432 andflange 434 which slide within slots through the pen housing. Theproximal face 435 of annular flange 434 is wedge shaped. When a userwishes to reset the drive screw 437, and after the cartridge assemblyhas been removed to access the extended drive screw, grip portion 432can be gripped and the collar manually pushed proximally, or down fromthe perspective of a FIG. 16 viewer, relative to the injector pen. Whenthe collar is so pushed proximally, wedge face 435 engages and forcesoutward L-shaped camming arms that are integrally formed with andproject radially outward from all of the flexible fingers of the driverand follower, such as camming arm 440 shown projecting from followerfinger 438. The forcing outward of the camming arms splays theirrespective flex fingers radially outward to disengage the threadedsegments of the flex fingers from drive screw 437, thereby allowing thedrive screw to fall or be manually pushed back, or be forced back duringcartridge mounting, in the proximal direction. When the proximal forceon collar grip portion 432 is released, the resiliency of the driver andfollower flex fingers causes the fingers to return to positions inthreaded engagement with drive screw 437, which return results in thecollar being forced upward to the ready position shown in FIG. 16. Anadditional biasing element urging the collar upward may be used in analternate embodiment.

[0123] In another drive screw reset mechanism that functions by splayingoutward the driver and follower fingers, a manually rotatable collarhaving an external grip portion disposed around the housing is provided.Within the pen housing, the collar includes axially depending, cammingprongs that ride within tracks provided on, for example, distal endfaces of the flex fingers of the driver and follower. The tracks areconfigured for camming action by the prongs, such that a manual twistingof the collar by the user in a first direction from a neutral angularposition to a camming angular position forces the driver and followerflex fingers radially outward to disengage the threaded segments of theflex fingers from the drive screw, which can then be pushed back. Whenthe user releases the collar, the flex fingers, due to their resilientconstruction, spring back to their ready positions in threadedengagement with the drive screw, thereby forcing the collar to twistfrom its camming position back to its neutral position.

[0124] In addition to the drive screw reset mechanisms of, for example,the embodiments of FIGS. 9-15 and FIG. 16 which function by disengagingthe driver and follower flex fingers from the drive screw threading,other mechanisms within the scope of the invention for resetting thedrive screw function by permitting the flex fingers to be rotated in areverse direction, preferably only when no medication cartridge ismounted, so as to essentially pull the drive screw back into thehousing. For example, portions of an injector pen that permits suchreverse rotation are diagrammatically shown in FIG. 17. The injector pen450 of FIG. 17 is similar in most respects to pen 220, but majorportions of pen 450, including but not limited to its follower and drivescrew, are not shown so as to more clearly illustrate the drive screwreset mechanism. The priming driver of pen 450 includes a resilient pawl454 formed on the distal surfaces of the base legs of the steppedportions 452 of the driver flex fingers. An annular clutch 456 isaxially movable within pen outer shell 458 and is prevented fromrotating therein by radially protruding keys 460 that slide withinlongitudinal keyways or recesses 462 within the shell. An annulararrangement of one-way clutch teeth 464 that mate with pawls 454 arelocated on the proximal face of clutch 456. Clutch 456 is shown beingbiased toward the distal or neutral position of FIG. 17 by a coiledspring 466. Although shown acting directly against driver steppedportions 452, spring 466 may be seated on a not shown, inwardlyprotruding shoulder of the outer shell. When the cartridge retainer 470is mounted by being screwed down into pen housing 458, the cartridgeretainer, or preferably the not shown cartridge loaded therein, abutsclutch 456 and forces it downward from the perspective of a FIG. 17viewer against the force of a compressing spring 466. When the cartridgeand retainer 470 is fully mounted, pawls 454 interface with clutch teeth464 to prevent the driver from rotating, from the perspective of aviewer of FIG. 17, in a clockwise direction. The resiliency of each pawl454 and the shape of its head allows the driver to be rotated in thedirection which advances the not shown drive screw for priming the peninjector, during which rotation the pawls slide over the clutch teeth464. When cartridge retainer 470 is removed to replace the spentcartridge, spring 466 forces clutch 456 distally such that teeth 464 areout of engagement with the driver pawls 454, whereby the driver can berotated to pull the rotatably fixed drive screw proximally into the pen.In this embodiment, the driver does not need additional pawls similar topawls 288 of injector pen 220.

[0125] The fixed dose delivered by operation of pen 20, or injector pen220, is preset at the factory, and therefore each of these pens isparticularly adapted to deliver a single dose for each complete axialwithdrawal and then plunging of its respective plunger. However, each ofthese types of pens can be manufactured differently to achievedifferent, individual fixed doses. For example, by modifying during penmanufacture the pitch of threading 84 or the locations of stops ribs120, different disposable pens 20 can each be provided with a different,individual fixed dose.

[0126] The present invention will find particularly beneficialapplication in delivering medicines in which the necessary dose is thepreset dose of the pen, or a small multiple of that preset dose.Moreover, if delivering an excess of medicine is not medicallyproblematic, such as in the case of a type of diabetes medicine known asglucagon like peptide-1(7-37), including analogs and derivatives thereofsuch as Val⁸GLP-1(7-37)OH, the use of the pen multiple times canintroduce slightly more than the desired dose. For example, in the caseof a medicine having two normal dosage amounts, such as eighteen unitsand fifty units, a single inventive pen adapted to dispense eighteenunits for each pull/push cycle may be used to deliver both dosageamounts. Specifically, with injector pen 20, a single complete axialwithdrawal and then plunging of plunger 160 can be used to delivereighteen units, while a series of three complete axial withdrawals andthen plungings of plunger 160 can be used to deliver fifty-four units,which is slightly greater than the needed fifty units.

[0127] The reusable injector pens, especially injector pen 220,described herein also may find particularly beneficial application in amedicine injecting system that utilizes a plurality of similar pens,each pen being adapted to deliver a particular fixed volume differentfrom the fixed volumes of the other pens in the system. Such a systemmay use different concentrations of the same medicine provided indifferent disposable cartridges, with each cartridge being intended fora particular reusable pen. To reduce the likelihood of improper amountsof medicine being injected, such a system may use cartridges fixedlyattached or integrated with their respective cartridge retainers, sothat the cartridge/retainer is disposable as a unit when its medicine isexhausted. And, each reusable pen and its associated cartridge/retainerhas a unique mounting or connecting means. For example, each model ofreusable pen may have a different pitch of its threading 257, such thata disposable cartridge/retainer intended for that reusable pen wouldonly fit that pen, and not other pens in the system. Consequently, nointerchangeability of retainers/cartridges between types of reusablepens exists. Furthermore, the integrated cartridge/retainer inconjunction with the pens with the unique design of, for example,threading 257 also serve to prevent loading the reusable pens with othertypes of medicines available in ordinary cartridges.

[0128] While this invention has been shown and described as havingpreferred designs, the present invention may be modified within thespirit and scope of this disclosure. This application is thereforeintended to cover any variations, uses or adaptations of the inventionusing its general principles. Further, this application is intended tocover such departures from the present disclosure as come within knownor customary practice in the art to which this invention pertains.

We claim:
 1. A medication dispensing apparatus comprising: a housing; afluid container mounted to said housing, said container defining amedicine-filled reservoir; a needle assembly removably attached to adistal end of said fluid container to have an injection needle of saidneedle assembly in flow communication with said reservoir; a drivemechanism for dispensing a dose of medicine from said reservoir throughsaid injection needle, said drive mechanism including a plunger manuallypullable relative to said housing in a proximal direction to shift theapparatus from a ready state to a cocked state, said plunger manuallypushable relative to said housing in a distal direction to forcemedicine out said injection needle while returning the apparatus fromthe cocked state to the ready state; a priming mechanism for primingsaid injection needle with medicine from said reservoir, said primingmechanism including a drive portion external to said housing to bemanually rotatable relative to said housing; and a rotation controllingmechanism that permits manual rotation of said priming mechanism driveportion in a first direction and as far as necessary to achieve priming,and that prevents manual rotation of said priming mechanism driveportion in a direction opposite to said first direction.
 2. Themedication dispensing apparatus of claim 1 wherein said primingmechanism drive portion is adjacent to and operable independently ofsaid plunger.
 3. The medication dispensing apparatus of claim 1 whereinsaid rotation controlling mechanism comprises a ratchet pawl and ratchetteeth acting between said housing and said priming mechanism.
 4. Themedication dispensing apparatus of claim 1 wherein said primingmechanism is configured to achieve priming whether the apparatus is inthe cocked state or the ready state, and without altering the dose to bedispensed by the drive mechanism if the apparatus is in the cockedstate.
 5. The medication dispensing apparatus of claim 1 wherein saidpriming mechanism comprises a threaded portion and a rotatably fixeddrive screw, said threaded portion internal to said housing androtatably fixed relative to said priming mechanism drive portion, saidthreaded portion in engagement with external threading of said drivescrew, whereby rotation of said priming mechanism drive portion rotatessaid threaded portion to force said drive screw to translate distallyand force medication from the reservoir.
 6. The medication dispensingapparatus of claim 5 wherein said threaded portion comprises a pluralityof radially resilient fingers integrally formed with said primingmechanism drive portion.
 7. The medication dispensing apparatus of claim1 wherein said drive mechanism comprises a follower and a rotatablyfixed drive screw, said plunger connected to said follower to be axiallyfixed together while allowing relative rotation therebetween, saidfollower including a threaded portion internal to said housing and inengagement with external threading of said drive screw.
 8. Themedication dispensing apparatus of claim 7 wherein said threaded portionof said follower comprises a plurality of radially resilient fingers. 9.The medication dispensing apparatus of claim 1 wherein said fluidcontainer comprises a disposable cartridge removable from the apparatusfor replacement, and further comprising means for resetting said drivemechanism to reuse the medication dispensing apparatus with areplacement cartridge.
 10. A medication dispensing apparatus comprising:a housing; a fluid container mounted to said housing, said containerdefining a medicine-filled reservoir; a needle assembly removablyattached to a distal end of said fluid container to have an injectionneedle of said needle assembly in flow communication with saidreservoir; a drive mechanism for dispensing a dose of medicine from saidreservoir through said injection needle, said drive mechanism includinga plunger manually pullable relative to said housing in a proximaldirection to shift the apparatus from a ready state to a cocked state,said plunger manually pushable relative to said housing in a distaldirection to force medicine out said injection needle while returningthe apparatus from the cocked state to the ready state; a primingmechanism for priming said injection needle with medicine from saidreservoir by manually rotating an element other than said plunger; andwherein said priming mechanism is operable to effect priming whether theapparatus is in the cocked state or the ready state, and withoutaltering the dose to be dispensed by the drive mechanism if theapparatus is in the cocked state.
 11. A medication dispensing apparatuscomprising: a housing; a fluid container mounted to said housing, saidcontainer defining a medicine-filled reservoir with a movable piston ata proximal end; a needle assembly removably attached to a distal end ofsaid fluid container to have an injection needle of said needle assemblyin flow communication with said reservoir; a drive member axiallyextending within said housing and movable distally to advance saidmovable piston toward said injection needle, said drive member, along anaxial cross-section, having a series of axially spaced projections; afollower portion engagable with said projections and having a resilientconstruction; a plunger operably connected to said follower portion andmanually pullable in a proximal direction to shift said plunger from afirst position to a second position, and manually pushable in a distaldirection to shift said plunger from said second position to said firstposition; said follower portion being axially shiftable by movement ofsaid plunger in said proximal and distal directions, wherein saidfollower portion bends radially outward and axially slides over at leastone projection of said drive member when said plunger is pulledproximally to shift from said first position to said second position,and wherein said follower portion, by abutment with a projection of saiddrive member over which said follower portion previously slid, advancessaid drive member distally when said plunger is pushed distally fromsaid second position to said first position; and a priming driveroperably connected to said drive member and including a drive portionexternal to said housing which is manually rotatable independently ofsaid plunger to axially advance said drive member to prime saidinjection needle with medicine from said reservoir.
 12. The medicationdispensing apparatus of claim 11 wherein said drive member is a screwwith external threading, and wherein said series of axially spacedprojections comprise passes of said threading of said drive screw. 13.The medication dispensing apparatus of claim 11 wherein said fluidcontainer comprises a disposable cartridge removable from the apparatusfor replacement, and further comprising means for resetting said drivemember to reuse the medication dispensing apparatus with a replacementcartridge.
 14. The medication dispensing apparatus of claim 13 whereinsaid resetting means comprises a camming element movable within saidhousing between a ready position and a camming position, whereinmovement of said camming element from said ready position to saidcamming position forces said follower portion to bend radially outwardto disengage said follower portion from said projections.
 15. Themedication dispensing apparatus of claim 14 further comprising a biasingmember urging said camming element from said ready position to saidcamming position, and wherein said camming element is operablyconnectable to said fluid container such that mounting of said fluidcontainer to said housing automatically shifts said camming element fromsaid camming position to said ready position against the urging of saidbiasing member, and such that dismounting said fluid container from saidhousing allows said biasing member to automatically shift said cammingelement from said ready position to said camming position.
 16. Themedication dispensing apparatus of claim 13 further comprising means forensuring a complete resetting of said drive member, said resettingensuring means comprising at least one over-center spring mechanismengagable with said drive member.
 17. A medication dispensing apparatuscomprising: a housing; a fluid container mounted to said housing, saidcontainer defining a medicine-filled reservoir with a movable piston atone end and an outlet at the other end; a drive screw with externalthreading, said drive screw axially extending within said housing andmovable distally to advance said movable piston toward said outlet; atleast one anti-rotation member operably engaging said drive screw toprevent rotation of said drive screw within said housing; a primingdriver axially retained relative to said housing and having a firstportion and a second portion, said first portion internal to saidhousing and in threaded engagement with said drive screw, said secondportion external to said housing to be manually rotatable, wherebyrotation of said second portion rotates said first portion to force saiddrive screw to translate distally; a follower axially movable relativeto said priming driver and rotatably fixed thereto, said followerincluding a portion internal to said housing and in threaded engagementwith said drive screw; a plunger axially movable relative to saidhousing between a distal position and a proximal position, said plungerincluding a manually graspable grip portion which is pullable proximallyto move said plunger from said distal position to said proximalposition, said plunger connected to said follower to allow relativerotation therebetween and to shift said follower axially when saidplunger moves back and forth between said distal and proximal positions;and wherein each of said follower portion and said priming driver firstportion comprises a resilient construction, whereby when said plunger ispulled from said distal position to said proximal position to shift saidfollower proximally, said follower portion slides over said threading ofsaid drive screw that is being axially retained by engagement with saidpriming driver first portion, and whereby when said plunger is pushedfrom said proximal position to said distal position to shift saidfollower distally, said priming driver first portion slides over saidthreading of said drive screw that is being axially advanced byengagement with said follower portion.
 18. The medication dispensingapparatus of claim 17 wherein said priming driver first portioncomprises a plurality of axially extending fingers angularly spacedaround a circumference of said drive screw.
 19. The medicationdispensing apparatus of claim 18 wherein said follower portion comprisesa plurality of angularly spaced, axially extending fingers that interfitwith said plurality of fingers of said priming driver first portion torotationally key said follower with said priming driver.
 20. Themedication dispensing apparatus of claim 19 wherein at least one of saidplurality of fingers of said priming driver first portion comprises aprojecting stop that abuts at least one of said plurality of fingers ofsaid follower portion to limit distal travel of said follower duringuse.
 21. The medication dispensing apparatus of claim 17 wherein saidpriming driver comprises a radially inwardly extending ledge that abutsa radially outwardly projecting shoulder of said follower to limitproximal travel of said follower during use.
 22. The medicationdispensing apparatus of claim 17 wherein said priming driver comprisesone of a ratchet pawl and ratchet teeth, and said housing comprises theother of the ratchet pawl and ratchet teeth, said ratchet pawl andratchet teeth interfitting to prevent rotation of said priming driverwithin said housing in a direction that would force said drive screw totranslate proximally.
 23. The medication dispensing apparatus of claim17 wherein said at least one anti-rotation member comprises a pair ofdiametrically opposed prongs that radially inwardly project from aninterior wall of said housing, said prongs fitting within a pair oflongitudinally extending slots formed in said threading of said drivescrew.
 24. The medication dispensing apparatus of claim 17 wherein saidfluid container comprises a disposable cartridge removable from theapparatus for replacement, and further comprising means for resettingsaid drive screw to reuse the medication dispensing apparatus with areplacement cartridge.
 25. The medication dispensing apparatus of claim24 wherein said resetting means comprises a camming element movablewithin said housing between a ready position and a camming position,wherein movement of said camming element from said ready position tosaid camming position forces said follower portion and said primingdriver first portion to bend radially outward to disengage said followerportion and said priming driver first portion from threaded engagementwith said drive screw.
 26. The medication dispensing apparatus of claim25 wherein said camming element comprises an inner ring, an outer ringand a plurality of arms connecting said inner ring and said outer ring,said inner ring positioned radially between said drive screw and bothsaid follower portion and said priming driver first portion, said outerring positioned within said housing radially outward of said followerportion and said priming driver first portion, and said connecting armsextending through angular gaps between said follower portion and saidpriming driver first portion.
 27. The medication dispensing apparatus ofclaim 26 wherein said outer ring is located distally of said inner ring.28. The medication dispensing apparatus of claim 25 further comprising abiasing member urging said camming element from said ready position tosaid camming position, and wherein said camming element is operablyconnectable to said fluid container such that mounting of said fluidcontainer to said housing automatically shifts said camming element fromsaid camming position to said ready position against the urging of saidbiasing member, and such that dismounting said fluid container from saidhousing allows said biasing member to automatically shift said cammingelement from said ready position to said camming position.
 29. Themedication dispensing apparatus of claim 28 wherein said camming elementis operably connectable to said fluid container by a separate interfacemember disposed within said housing distally of said camming element,said interface member comprising a cartridge abutting surface and acamming element abutting surface.
 30. The medication dispensingapparatus of claim 25 wherein said camming element comprises a gripportion and a camming portion, said grip portion external to saidhousing and connected to said camming portion internal to said housing.31. The medication dispensing apparatus of claim 30 wherein said cammingelement translates axially when shifted from said ready position to saidcamming position.
 32. The medication dispensing apparatus of claim 24further comprising means for ensuring a complete resetting of said drivescrew.
 33. The medication dispensing apparatus of claim 32 wherein saidresetting ensuring means comprises at least one over-center springmechanism engagable with said drive screw.
 34. The medication dispensingapparatus of claim 33 wherein said at least one over-center springmechanism comprises at least one spring loaded pivotable memberincluding a tip portion that slides within a longitudinally extendingslot formed in said threading of said drive screw, and wherein saidpivotable member automatically pivots from a first position to a secondposition when said tip portion inserts within a recess formed in saidslot and acts against a ledge surface of said drive screw which definessaid recess.
 35. The medication dispensing apparatus of claim 34 whereinsaid ledge surface comprises a surface defining a throughbore throughsaid drive screw.
 36. The medication dispensing apparatus of claim 34wherein said at least one spring loaded pivotable member comprises firstand second pivotable members each including a tip portion that slideswithin a different longitudinally extending slot formed in saidthreading of said drive screw.
 37. A medication dispensing apparatus(20) comprising: a housing (60); a fluid container (28, 48) mounted tosaid housing, said container defining a medicine-filled reservoir (50);a needle assembly (38) removably attached to a distal end of said fluidcontainer to have an injection needle (40) of said needle assembly inflow communication with said reservoir; a drive mechanism for dispensinga dose of medicine from said reservoir through said injection needle,said drive mechanism including a plunger (160) manually pullablerelative to said housing in a proximal direction to shift the apparatusfrom a ready state to a cocked state, said plunger manually pushablerelative to said housing in a distal direction to force medicine outsaid injection needle while returning the apparatus from the cockedstate to the ready state; a priming mechanism for priming said injectionneedle with medicine from said reservoir, said priming mechanismincluding a drive portion (102) external to said housing to be manuallyrotatable relative to said housing; characterized in that saidmedication dispensing apparatus further comprises a rotation controllingmechanism (68, 106, 108) that permits manual rotation of said primingmechanism drive portion in a first direction and as far as necessary toachieve priming, and that prevents manual rotation of said primingmechanism drive portion in a direction opposite to said first direction.38. The medication dispensing apparatus (20) of claim 37 wherein saidpriming mechanism drive portion is adjacent to and operable indepedentlyof said plunger.
 39. The medication dispensing apparatus (20) of claim37 wherein said rotation controlling mechanism comprises a ratchet pawl(106, 108) and ratchet teeth (68) acting between said housing and saidpriming mechanism.
 40. The medication dispensing apparatus (20) of claim37 wherein said priming mechanism is configured to achieve primingwhether the apparatus is in the cocked state or the ready state, andwithout altering the dose to be dispensed by the drive mechanism if theapparatus is in the cocked state.
 41. The medication dispensingapparatus (20) of claim 37 wherein said priming mechanism comprises athreaded portion (128, 132) and a rotatably fixed drive screw (80), saidthreaded portion internal to said housing and rotatably fixed relativeto said priming mechanism drive portion, said threaded portion inengagement with external threading (84) of said drive screw, wherebyrotation of said priming mechanism drive portion rotates said threadedportion to force said drive screw to translate distally and forcemedication from the reservoir.
 42. The medication dispensing apparatus(20) of claim 41 wherein said threaded portion comprises a plurality ofradially resilient fingers (128) integrally formed with said primingmechanism drive portion.
 43. The medication dispensing apparatus (20) ofclaim 37 wherein said drive mechanism comprises follower (140) and arotatably fixed drive screw (80), said plunger connected to saidfollower to be axially fixed together while allowing relative rotationtherebetween, said follower including a threaded portion (146, 148)internal to said housing and in engagement with external threading (84)of said drive screw.
 44. The medication dispensing apparatus (20) ofclaim 43 wherein said threaded portion of said follower comprises aplurality of radially resilient fingers (146).
 45. The medicationdispensing apparatus (220) of claim 37 wherein said fluid containercomprises a disposable cartridge (238) removable from the apparatus forreplacement, and further comprising means (385, 387, 389) for resettingsaid drive mechanism to reuse the medication dispensing apparatus with areplacement cartridge.